How did you set them up? Through the web page, software or MWS ?
I would guess most would default to starting at 0:00:00 but it could be that the time you actually set the date was also used.
i.e. You set up the listing after you ate lunch at say 1:30 PM.
So the start could be 2012-02-11T13:30:00Z (basically)
The Seller Account page has 'Start selling date: ' so if set to 02-11-2012 then they should be showing
Software and MWS ... it could be appending the time you actually created the listing